Information volumes to be handled by mobile phones with a movie capturing function, digital cameras exceeding six million pixels, and the like are rapidly increasing year by year, and an increase in capacity and a size reduction of information recording devices are demanded. A direct method of increasing the recording density of an information recording device is to reduce the size of a recording or reproduction bit in a hard disk or optical disk, and to reduce a unit cell size in a nonvolatile memory such as a flash memory. However, the method based on the existing principle (e.g., diffraction of light) encounters the physical limits of density enhancement in the near future. For example, in case of a hard disk drive, since the heat fluctuation influence of magnetism becomes more serious as the density increases, data may be destroyed at room temperatures if the density is simply increased under the present circumstances. Even in case of an optical disk, the size of a recording or reproduction bit approaches its limit due to a diffraction limitation of light. As a dominant measure that can break through such limits, a probe type MEMS memory using the principle of the scanning probe microscopy (SPM) has been studied.
The probe based memory device is a recording device in which probes are employed to write, read out, or erase information using various interactions between recording or reproduction electrodes of probe tip and a recording medium. When a microprobe is employed as a recording or reproduction head of the probe based memory device, some important factors such as a charge, resistance, current, and voltage have to be precisely measured by the microprobe. For this reason, it is important to assure the stable contact state between the microprobe tip and a recording medium at the time of recording or reproduction. When the contact state is insufficient, the recording or reproduction operation becomes unstable, thus causing a reliability drop of the probe based memory device. For this reason, it is important to ensure that the recording or reproduction electrodes contact recording medium at the time of recording or reproduction. In other words, it is important to eliminate a possibility of an unstable contact state between the recording or reproduction electrodes and the recording medium at the time of recording or reproduction.
Conventionally, in order to allow the probe based memory device to record or reproduce information at a high speed and high density, a sharpened type probe is usually employed. In this case, the size of the probe tip normally ranges from several nanometers to several hundred nanometers. The probe with a small tip size is much easier to wore out than a probe with a large tip when the same force is applied, resulting in a change in tip size. This will cause a change of recording or reproduction bit when the wore probe operates recording or reproduction behavior. As the wear progresses, the probe tip may not be able to operate recording or reproduction behavior or keep the stable contact state with the recording media, disabling the recording or reproduction operation.
The third page of JP-A 2006-221792 (KOKAI) describes experimental results about such wears of the probe tips. This experiment observes wearing state when the same load is applied to the sharpened type probe with a tip radius of 5 nanometers, and the blunt type with a tip radius 50 nanometers. The moving velocity of the probe is 2 μm/s. As can be seen from the experimental results, when the same load is applied, the sharp type probe is considerably worn compared to the blunt type. This is because the tip radius of the sharpened type probe is smaller than that of the blunt type, causing a concentration on the smaller tip when the same load is applied. Since the sharp type probe can write and read out a smaller recording or reproduction bit than the blunt type, a high-density recording device normally have to adopt the sharpened type.